Ignition system for internal combustion engines



Feb. 9, 1943. A. G. cATTANEo Filed may 27, 1940 IGNITION SYSTEM FOR INTERNAL CDMBUSTION ENGINES Flifer n@ and Umm@ umL Pump Passed Feb. 9, 1943 IGNITION SYSTEM FOR INTERNAL COMBUSTION ENGINES Alfred G. Cattaneo, Berkeley, Calif.,

Shell Development Company, San

assignor to Francisco,

Calif., a corporation of Delaware Application May 27, 1940, Serial No. 337,416

Claims.

The present invention relates to an improvement in ignition systems for internal combustion engines and particularly to a method and apparatus for cooling the central electrode of spark plugs of internal combustion engines utilizing spark ignition.

It is known that when spark ignition engines are heavily loaded in operation, the electrodes of the spark plugsmay become suiliclently overheated to cause pre-ignition, detonation and similar forms o! uncontrolled combustion. 'I'hls trouble is encountered especially with gasoline engines, particularlyv owing to the central electrode, for this electrode must be electrically insulated from the body of the spark plug by means of materials which in most instances are also heat insulators. Whereas the body of the spark plug can be cooled by metal fins which are exposed to the air, this is not the case with the central electrode, since the latter is not only largely enclosed in the body of the spark plug, but the projecting part is frequently surrounded by a radio screening device as well.

It is also known that a large part of the igniu tion troubles encountered in aircraft engines and formerly attributed to faulty spark plug operation has in reality been caused by the high tension cables leading from the current source to the spark plugs due to the presence of moisture in the cable harness, the tendency to high tension cable breakdown at high altitudes, and other factors which tend to permit at least a temporary short circuit between the grounded metal harness and the cables themselves.

It is an object of the present invention to provide a system and vapparatus whereby both of these common diiilculties are overcome in a related manner. |Further, it is an object of the instant invention to provide a spark plug of improved design, particularly suitable for use according to the `system to be described. Still further, it is an object to provide means whereby these diiliculties are overcome with but slight modification of equipment already normally existent in aircraft engines.

It has already been proposed to cool spark plug electrodes in internal combustion engines by making the electrodes hollow and drawing air from outside into the cylinders through the electrodes during the suction stroke of the piston. In this case the conduits leading from the atmosphere to the cylinder space through the electrodes must be provided with non-return valves of one sort or another to prevent. air or combustion gases from being driven out during the tral spark plug electrode which is closed towards the cylinder space. The internal hollow electrode is, therefore, not in communication with the cylinder space, so that there can be no escape of hot combustion gases through the electrode. As a coolant, dry air is quite suitable; it is a satisfactory electric insulator and further, in the present case will be supplied to the hollow electrode under pressure, the electrode being thus easily kept within the desired operating temperature range of 500 to 800 C.

It has also now been found that by pressurizing the so-called harness," which consists oi metallic tubing suitably formed and which serves to protect the spark plug cables, most of the heretofore encountered trouble with short circuiting between the harness and the cables may be eliminated. In the present invention air under pressure from a pressurized harness is utilized as a coolant for the central electrode of the spark plugs, as will be more clearly understood from the following description of the appended drawing.

Figure I is a sectional elevation of a spark plug especially adapted for use according to the invention.

Figure II is a diagrammatic drawing of a pressurized harness as utilized according to the invention.

Referring particularly to Figure I, the spark plug comprises a bushing-shaped part I including an earthed electrode 2, a central body 3 with the central electrode I, which is insulated by insulating material 5, 5a, 5b, 5c from the body 3 of the spark plug. 'Ihe part of the central body projecting from the cylinder is provided with cooling ilns.

Electrode l is provided with a cavity extending to the bottom end thereof. and a tube 8 is fitted within this cavity projecting to the bottom of the same, where it is split and equipped with tongues bent outwards to center it as at 1. The top of the tube 8 is widened and is subjected to the action of the spring 8 which tends to urge the tube upwards. As a result the tube 6 is pressed against the hollow contact piece 9, which both established electric contact between pressing only air, the air pump I8 shown is 4 V5 lbs. per square inch, this pressure having been It and conveys cooling air to tube Irfrom the space between cableJIl and the harness tube il.

`Harness tube II is fastened to the electrode body 3 by means of a cap nut I2. -Care mustvoi course be taken that contact piece Oris linsulated with respect to the grounded portion of the v spark plug. To this end the intermediate-piece Il, Vprovided with air ducts Il. should zbe made` on non-conductive material. Near itsrtop, the

to the atmosphere. The hollow contact piece 9 sis also provided with openings as at I8 to permit ingress of air to tube 6.

In Figure II, each cylinder as at 24 of a radial aircraftengine is supplied with a spark plug Ii constructed as shown 'in Figure I. A harness lead as at -II extends from each spark plug to the harness manifold I8. High tension cables .lead from a distributor 2| through a sealed conduit l23 to the harness manifold I8 and 'thence to ea'ch spark plug through harness leads as at II. An air pump I9 including a unit 20 for drying and cleaning purposes supplies compressed air through a sealed conduit 22 to the harness mani- Vfold I8. If the engine or auxiliary equipment already includes a source ot compressed air, as for example in airplanes utilizing pressurized cabins or those wherein fuel injection for the engines is used, the supercharger in such cases comnot necessary.

In operation, suilicient air is supplied to the manifold harness Il and harness leads (as at II) to maintain a positive pressure upon the high tension cables to the spark plugs oi' approximately found satisfactory for most operating conditions to inhibit short circuiting. The air pressure within the harness will of course depend upon the volume and pressure of air supplied to the harness as well as the resistance to air flow through the spark plugs. Therefore, in operating a given engine according to the invention the iiow resistance through the spark plugs should be modified (for example by varying the size of the orifices at Il, I or I5) so that a sufficient amount oi.' air is passed through the spark plugs for cooling purposes and at the same time enough resistance to air flow is provided to maintain the desired pressure in the harness around the high tension cables. A

The conditions mentioned previously herein, i. e., sufficient. air to control the spark plug Vtemperature between 500 and 800 C. and at the same time maintain an approximate 5 lbs. vper square inch pressure in the harness will be found satisfactory in most instances.

rcentral body 3 is provided withl openingsV Il, through which the air which has passed throughl tube 8 of the central electrode and then through Vthe annular space around this tube can escape `gines comprising in combination a spark plug in- Y cluding a hollow central electrode closed toward the Bring end. a cable leading from a source oi high tension current to said spark plug,.a har` ness enclosing said cable and means adapted to f continuously pass a gaseous coolant under pressure'into said harness and through said hollow central electrode oi said spark plug.

- 'n 2.A Ignition means for internal combustion en- ;g'ines comprising in combination aspark plug including a hollow central electrode closed toward the iiring end, a tube in said hollow electrode oi substantially lesser diameter than the inside diameter'of said hollow electrode, communication means between the interior of said tube and the space between said tube and the inner wall oi said hollow electrode near thewiiring end of said 20 hollow electrode, communication means between said space and the atmosphere, a cable leading from .a source of hightension current to said spark plug, conductive means forming a contact between said "cableand said hollow central electrode, a` harness enclosing said cable, means for continuously supplying gaseous coolant under pressure to said harness and means connecting said harness and said tube adapted to permit passage of gaseous coolant from said harness to said tube. Y

3. Ignition means for internal combustion engines comprising in combination a spark plug, a hollow central electrode in said spark plug closed toward the ring end, a4 cable leading from a source of high tension current to said spark plug, a harness enclosing said cable, means adapted to continuously pass a gaseous coolant under pressure into said harness, a connecting passageway between said harness and the firing end of said hollow central electrode, an independent connecting passageway between'the firing end of said hollow electrode and the atmosphere, said'passageways being arranged and adapted to provide sufilcient resistance to gas flow to maintain a pressure in said harness.

4. The method of operating the ignition means of a spark-fired internal combustion engine utilizing a spark plug adapted `to permit passage of a gaseous coolant therethrough and a harness enclosed high tension cable leading to said spark plug comprising continuously supplyinga gaseous coolant under pressure to said harness and from said harness to said spark plug, a sufiicient gaseous pressure being maintained in said harness to inhibit the tendency to high tension cable inch.

ALFRED G. CATTANEO. 

